Differential relay and restraint magnet therefor



April 20, 1948. a. v. HOARD DIFFERENTIAL RELAY AND RESTRAINT MAGNETTHEREFOR Filed Ot. 10, 1942 INVENTOR B677 l/Haard ATTORNEY Patented Apr.20,1948

DIFFERENTIAL RELAY AND RESTRAINT MAGNET THEREFOR Bert v. Hoard,Portland, one, assignor to West inghonse Electric Corporation, EastPittsburgh, Pa., a corporation of Pennsylvania Application October 10,1942, Serial No. 461,577

My present invention relates to an improved type oi. electromagnet,which may be constructed in any one or several diflerent forms, withslightly different characteristics; and the invention also has relationto a particular differential altemat lug-current relay utilizing one ora plurality of these electromagnets in an apparatus and system which isparticularly useful in differential busprotection involving a largenumber of feeders, and for other uses.

My improved electromagnet or electro-responsive device consists of a,cylindrical magnetic core surrounded by a coil and having two flatpolepieces, one at each end the core and coil, the pole-pieces extendingout from the core and terminating in tapering ends; the movable part ofthe relay or other electro-responsive device being in the form of a thinfiat rectangular magnetizable armature spaced from the coil in parallelrelation thereto, and movable toward and away from the coil, between thetwo tapered ends of the polepieces. The tapering of the ends of thepole- 24 Claims. (Cl. 175-294) Among the objects and advantagesobtainable by my invention may be mentioned simplicity of manufacture, ahigh torque with a small weight or inertia, which means a high speed ofoperation, a high torque with a small volt-ampere requirement, whichmeans high eiiiciency and a small burden on the potential orcurrent-transformer which supplies the device with energy, constancy ofmagnetic pull at all positions of the movable armature, or any othercharacteristic of the pull with respect to the position or movement ofthe armature, and responsiveness to either the first power or the squareof the magnetizing-current, depending upon the nature of the core whichis utilized. In the differential-relay embodiment, my invention makes itpossible to differentially protect an eight-circuit bus or othermulti-ter-' minal apparatus, with a single relay per phase, and with avery simple system of wiring connecgo tlons, accomplishinga variablefatio difierential pieces makes it possible to maintain a constant pullon the armature at all positions of the armature, or to maintain aradually increasing or decreasing pull, as the armature moves in eitherdirection. By an alternative construction which makes provision forprogressive saturation in the core, the relay or electro-responsivedevice can be made to develop a force or pull which is practicallyexactly proportional to the first power of the magnetizing current, overa wide range of current-values from zero to over 120 amperes, ascontrasted with the force proportional to the square of the current,which is developed in most current-responsive devices.

My new electromagnet or electro-responsive device is extremely compact,and lends itself admirably to being associated either with other deg myinvention consists in the apparatus, parts,

combinations, circuits, systems and methods hereinafter described andclaimed and illustrated in the accompanying drawing, wherein:

Figure 1 is a plan view of a variable-ratiodiii'erential relay embodyingmy invention,

Fig. 2 is an elevational view thereof, with parts broken away toillustrate the construction,

vices of the same nature, or with diflerent kinds 4o ofrelay-elements,with one or more or the novel electromagnet-devices utilized asrestraint-elements, for example.

In particular, my present invention hasreference to a saturating type ofcurrent-responsive relay having two parts, an operative-iorce-producingpart which responds linearly to the current up to a certain value ofcurrent, after which the response falls off due to saturation, and arestraint-force-producing part comprising a plurality of my novelelectromagnets utilized as restraint-elements responding linearly to thecurrent in individual feeders, with the totalized bus-- current beingsupplied to the Operating-coils of the operating part of thecurrent-responsive relay.

be utilized as alternatives of the construction Fig. 3 is a diagrammaticview of the circuitconnections for the difierentlal relay shown in Figs.1 and 2, with diagrammatic representations explanatory oi theconstruction and operation of the several parts of the relay.

Figs. 4 and 5 are detail views of different poleplece shapes for theelectromagnet, which may be utilized to obtain difler'enttorque-response characteristics with respect to the position or movementof the movable armature, and

Figs. 6 and 7 are detail side views of different forms ofelectromagnet-constructions whlchmay shown in Figs. 1, 2 and 3.

The diiferential relay shown in Figs. 1 and 2 consists essentially oftwo diil'erent parts, associated with a vertical shaft [0' carrying amovable contact-arm ll cooperating with stationary contacts I! which areconnected in the relaycontrolled circuit IS. The upper part of the relayconsists of eight (or other number) of my special electromagnets Ml toM8, arranged (as shown) in two tiers l 4 and I, one above the other.

The bottom part of the relay consists of a special" high-speedinduction-disk element 18, of a type which is specifically described,and which is claimed, in my copending application Serial No. 456,901,filed September 1, 1942, for High-speed relays, now Patent No.2,379,905, issued July 10,

The eight magnet-structures Ml to M8 of Figs. 1 and 2 are all alike, andthey are also shown in side-elevational view in Fig. 3. As shown in Fig.3, they are utilized as restraint-elements responsive to the currents inindividual feeders Fl to F8, which are connected to a, common bus B;while the actuating or operating-torque of the relay is provided by thedisk-type current-responsive element l6 which is energized in responseto the summation or total of all of the feeder-currents as supplied bythe respective current-transformers CTI to GT8.

Each of the electromagnets, such as the electromagnet M4, comprises acore which is made up of a thin-walled steel or other magnetizable tube20 which is tapped throughout its length, thus making a series ofnotches along the face of its bore or inner diameter. Iron or othermagnetizable screws 2| and 22 enter the tapped tube 20, from therespective ends thereof, and thus provide an additional iron area nearthe ends of the tube, the central portion of the tube beinghollow, andnot filled with magnetizable material. The ta ped tube 20 is surroundedby an energizing-coil 28 for the electromagnet. Abutting against therespective ends of the tapped tube 20, are two fiat pole-pieces 24 and25, which extend out away from the core 20 and from the coil 28, andwhich terminate in diagonally cut ends 28, as shown in plan view inFig. 1. The pole-pieces 24 and 25 may be held in place by the screws 2|and 22, respectively, and one of these screws, as 22, may also beutilized to mount the device on a stationary supporting-plate 21, asshown in Fig. 2. Preferably, the pole-pieces 24 and 25 should beslotted, as shown at 24' and 25' to reduce theeddy-current lossesresulting from the alternating flux in the core 20.

The movable element of" each electromagnet, such as the electromagnetM4, consists of an armature 28 which is in the form of a thin flatrectangular piece of magnetic material, mounted on' an arm 29 carried bythe shaft l0, at right angles to the shaft. The armature 28 extendsbetween the two tapered ends 28 of the two pole-pieces 24 and 25, withsmall airgaps 8| between the respective ends of the armature 28 and theinner surfaces of the pole-pieces 24 and 25, respectively. The armature28 is disposed in a plane substantially parallel to the core 20, and thecore 20 is vertical, or parallel to the shaft in which constitutes thepivot-point for the armature-arm 29, so that the armature 28 moves in adirection toward and away from the core 20 and its magnet-coil 23.

The bottom half of the relay shown in Figs. 1 and 2 constitutes thecurrent-responsive membar [6 which provides the operating torque forturning the shaft III in a direction necessary to make the relayrespond, as by closing its contacts il-I2. The current-responsiveoperating-element I6 comprises a disk 88 which is carried by the shaft[0, at right angles thereto, and is actuated upon by two multipoiarstator-portions 84 and '35, respectively, one abovethe disk 83 and theother below the disk 88.

The upper multipoiar structure 34 comprises four pole-pieces, eachhaving a vertical tubular 4 magnetlzable pole-shank 88 extendingparallel to the shaft [0. Each pole-shank 88 terminates, at its bottomend in a segmental magnetizable poleface portion 4| which is spaced fromthe upper surface of the disk 38 by an airgap 42. Each pole shank 88terminates, at its upper end, in a ringshaped magnetizable yoke-member48 which joins the upper ends of all four of the pole-shanks 88 of theupper multipoiar structure 84. The parts Just described can be held inassembled position,

.and also mounted on a horizontal support-plate 44, by means of bolts 45which pass thro gh Poles 46 in the yoke-member 48, and also pass throughthe tubular pole-shanks 88, screwing into the pole-face pieces 4| of therespective poles of the upper multipoiar structure 84.

The lower multipoiar structure is similar, except that the tubularpole-shank portions 88" are thicker, and the energizing-coils 48' arelarger, consisting of more turns suitable for voltage-responsiveenergization as distinguished from the current-coils of the uppermultipoiar structure. In the lower multipoiar structure, also, theyoke-member 43' is a solid disk, as distinguished from thering-structure 48 of the upper multipolar member.

-ly saturable autotransformer 50.

The several pole-pieces of the upper and lower multipolar structures 84and 85 are displaced with respect to each other in substantiallyquadrature space-relationship, as indicated in Figs. 1 and 2, and alsoas diagrammatically illustrated, in a development view, in Fig. 3.

I As shown in Fig. 3, the current-coils 48, and the voltage-type coils40 of the operating-element 48 are energized from a special,progressive- The transformer 50 has an iron core 5|, one portion ofwhich is provided with a taperingly reduced cross-section as indicatedat 52, so as to produce progressive saturation, starting at low valuesof the exciting-current which traverses the transformer-winding 53.Thus, as the transformercurrent gradually increases from zero, thenarrowest portion of the restricted section 52 firstsaturates, and thissaturation creeps along for a greater and greater distance, as theexcitingcurrent increases. The autotransformer has a high-currentintermediate tap 54 which is utilized to energize the current-windings40, and a lowcurrent terminal 55 which energizes the voltagetypecurrent-responsive coils 48' through a phase-adjusting resistor 55.

In the operation of the apparatus and circuitconnections shown in Figs.1, 2 and 3, attention will be directed, first, to the electromagnets,such as the electromagnet M4. The movable armature 28 has its endspresented (through airgaps) to the triangular or tapered portions 28 ofthe two pole-pieces 24 and 25 of the electromagnet. Because of thetriangular or tapered configuration of these pole-piece ends, the fluxflowing from each pole-piece to the end of the armature 28 is larger, onthe side of the armature which is presented toward the magnet-core 28,than on the side of the armature furthest away from said core. The fluxon the core side tends to pull the armature toward the core, with aforce proportional to the square of this flux, while the flux on theopposite side tends to pull the armature away from the core, or towardthe pointed tips of the ends of the pole-pieces, with a force which isagain proportional to the square of the flux. Because of the taperedshape of each poleforce which is approximately proportional to thesquare of the flux-density, times the difference between thecross-sectional areas of the effective airgaps on the two sides of thearmature 28' that is, on the side towards the. core 28, and on the sideaway from the core 28, making due allowancefor the fringing of the fluxin the airgap, on each side of the armature 28.

If the tapering of the end-portion 28 of the pole pieces 24 and 25 isuniform, as shown in Fig. l, and if the effective radius of theturningmoment operating on the armature-supporting arm 28 does notmaterially change throughout the range of movement of the armature 28,then the total effective operating-moment which tends to draw thearmature 28 toward the core 28 will be constant at all positions of thearmature 28, for any given strength of energization of the magnet-coil23. If the efiective turning-moment operating on the armature-supportingarm 28 changes during the movement of the armature 28, this change inturning-moment can be compensated for by suitably shaping thepole-pieces, as shown in Figs. 4 and 5.

It will be readily understood that if it is desired to have a largerforce, which remains substantially constant over a smaller distance ofmovement of the armature 28, the tapering of the tapered ends 26 of thepole-pieces can be made more sharp than the tapering shown in Fig. 1, sothat the airgap-sectlon increases at a faster rate, as the armaturemoves toward the core of the magnet. If it should be required that thetorque should increase, as the armature moves toward the core, the shapeof the pole-pieces should be modified so that the rate of increase ofthe airgap-section increases, as the armature approaches the core, asshownat 26' in Fig. 4. If it should be required that the torque shoulddecrease, as the armature is attracted toward the core, the pole-pieceshape should be modified so that the rate of change of theairgap-section, or the rate of change of this width of each pole-piece,shall decrease, as the armature approaches the core, as shown at 26" inFig. 5.

In any event, it will be noted that the electromagnet M4 is simple tomake, and that it provides a means whereby the operating-force producedby the magnet shall be either substantially independent of thearmature-position, or

mils, or less, and about 60 mils, another important advantage accrues,as a result of the fringing of the flux at the airgaps 8!, asdiagrammatically indicated at I! in the electromagnets shown in Fig. 3.From this figure, it will be seen that the fringing, or spreading out ofthe flux as it leaves the respective ends of the armature 28 and entersthe tapered polepieces, on both the core side of the armature 28 and theopposite side of the armature, produces the same effect as if thearmature were several times thicker than it is, but without the fringingof the magnetic flux. Thus the fringing causes the airgap-area to becomeseveral times, or at least four or five times, the iron area presentedby the respective ends of the thin armaturemembers 28.

Since the magnetic forces operative upon-the armature are proportionalto the square of the total flux, and since the amount of fiux isproportional to the effective airgap area, it will be noted that thisfringing of the flux, which produces at least a fourfold increase in theairgaparea, produces a corresponding increase in the amount of themagnetic pull or attraction, thus producing a larger force, incomparison to the mass or inertia of the armature, than would be thecase without fringing. This effect has two important advantages, in thatit increases the operating-force, and hence the sensitivity of theelectro-responsive device, for any given voltampere burden on thepotential or currenttransformer which supplies energy to the device,

in accordance with any other predetermined torque-characteristic withrespect to armatureposition.

The rectangular-shaped magnetizable armature-piece 28 should have assmall a cross-section as possible, so as to decrease the mass or inertiaof the movable element, particularly in electromagnet-structures where ahigh speed of operation is desirable, which means a large ratio ofoperating-force to inertia. Thus, the relay or electromagnet would bedesigned so that the cross-section of the main part of the armaturepiece28 will just begin to approach saturation,

at the full rated voltage of the magnet-coil 23,

if the electromagnet is utilized as a voltage-responsive device, or toapproach saturation at the maximum expectable current therein, or at anysmaller predetermined current-value, if the electromagnet is utilized asa current-responsive device.

When the armature-piece 28 is made of a sheet of iron or steel having athin thickness, such as the thickness of one ordinary lamination, whichis 15 mils, or a thickness of, say, between 15 and it also increases theratio of force to inertia, which means an increased speed of operation.

In cases where still greater operating forces are desired, it isfeasible to increase the effective thicknesses or cross-sections of theextreme ends of the armature-piece 28, without changing the sectionalarea of the main portion of the armature-piece. In this manner, theairgapsection can be increased, without materially increasing the massor inertia of the armature. A convenient manner of carrying this ideainto execution is indicated in the armature-piece 2B of Fig. 6, whereinthe ends of the armature are .bent over, as indicated at 60 in Fig. 6.This modified form of construction of the armature, with bent-over ends68, may be utilized in any of the embodiments of my invention.

Thus far, I have been specifically discussing the torque-characteristicsof the electromagnet M4 with reference to the armature-position and thearmature-inertia, without reference to the effectiveness of theenergization or magnetization of the electromagnet.

Reference to Fig. 3 will show that the screwthreads which are tappedinto the thin walled steel tube 20 which is utilized for the core of theelectromagnet produce a plurality of wedgeshaped sectional areas, or aniron-section which progressively increases and decreases along thelength of the core, at least along the central portion of the tappedcore-tube 20, which is not filled with the iron screws 2| or 22. By athinwalled, tapped, tube 20, in this case, I thus mean a tube in whichthe walls are thin enough so that the threads which are tapped into thetube will be fairly deep, as compared to the thickness of thetube-walls, so that a fairly large proportionate decrease in theeffective section shall be produced by the threads. I also contemplatethat the threads shall be triangular-shaped, rather than square-shaped,or of any other shape. It is apparent that the notches produced 7 by thescrew-threads will produce portions of the tube walls, at spaced pointsalong the length 01' the tube, which will progressively saturate, withincreasing magnetizing current, until the thickest section is saturated.The design is such that the saturation commences at a small value or theenergizing-current, and progresses in its extent, as theenergizing-current increases.-

The exact characteristics of the saturationefiects in the magnets Ml toM8 can conveniently be determined by the length or the iron screws 2|and 22' which enter the tube 20 from the respective ends thereof. In oneparticular electromagnet, tests have shown that when each screw entersabout 25% of the tube length, the

flux increases so slowly in response to increases in theexciting-current, that the square of the flux, which determines themagnetic pull developed by the electromagnet-structure, respondssubstantially rectilinearly to the current, for all current-values fromzero to 120 amperes, thus producing a response to the first power or thecurrent, as distinguished from a response to the square of the current,which would be obtained if no saturation were present. Thesaturationefiects can be strengthened by having each screw enter only ashorter distance, say about of the tube length, whereas, if each screwenters a greater distance of the tube-length, say about 40%, themagnetic torque is approximately double the value which it would havewhen the screw enters the tube about 10% of the total tube-length,although the current-responsive curve is not quite as straight for allcurrentvalues as when each screw enters about 25% of the tube-length.This constitutes a simple method of controlling the torque of theelectromagnet, although the torque can also be controlled by changingthe number of turns on the coil 23.

The tapered eiTect of the progressively saturable iron section, which isproduced by the screw-threads tapped into the thin-walled steel tube 20,may be produced in other ways. Thus, in Fig. 6, the core 20 is producedby machining down the outer diameter of the tubular or cylindrical core20', to produce a single reduced-section point Bl near the center of thecore, which gradually increases in diameter or cross sectional areatoward the ends of the core. In this manner, by properly choosing therate at which the coreseotion increases from its .most restricted point,substantially the same saturatlon-efiects can be obtained as havealready been described, thus producing an electro-responsive devicewhich produces an operating torque which is either linearly responsiveto the first power of the current, or responsive in accordance with someother predetermined function.

In many applications of my electro-responslve device, such as M4, therectilinear, or first-power response is important. tions, however, it isdesirable to have the more sual-type of response, in which the forcevaries as the square of the current. In such a case, the core 20 may bemade tohave a sufilcient thickness so that it will not saturate, asshown in Fig. 7, in which case the core may be a solid cylinder, ratherthan a tube, or if it is a tube, it will have 4 thick, non-saturablewalls, and the inner bore of the tube could be either smooth or tapped,so long as the tapped screw-threads did not reduce the core-section:sufiiciently to produce saturation.

In the particular application of my novel electromagnet-structurewhich'is shown in Figs. 1, 2

In many other applica-- and 3, the rectilinear response 01 eachelectromagnet to the first power or the exciting-current is quiteimportant, because the electromagnets Ml to M8 are utilized to developrestraint-torques which are responsive to the currents in the respectivefeeders or terminals Fl to F8 of an alternating-current bus B, in adiflerential busprotecting relay in which an operating-force is producedin accordance with the vectorlal sum,.

or instantaneous totals. of the currents flowing into the bus at all ofits terminals or feeders Fl to F8, regardless of whether those feedersare normally power-supplying feeders or load-feeders. .By making theindividual restraint-torques responsive to the first power or thecurrents in the respective feeders or terminals, the sum-total of allthe restraint, for any given total current, will be the same regardlessof the distribution of that current along the several terminals orfeeders Fl to F8, whereas, if the restraint-torque were responsive tothe square of the currents in the respective feeders, the total amountof restraining torque of all eight electromagnets would be eight timesmore, if all of the current were carried by a single feeder, than if thetotal-current were divided equally among the eight feeders.

In the differential relaying device shown in Figs. 1, 2 and 3, it isdesirable that the operatingforce, by which is meant the force tendingto actuate the relay in opposition to the back-pull of the restrainingforces, shall also be responsive to the first power of the current (orother electrical quantity to which the relay is difierentiallyresponding), but it is also desirable that the operating-force-responseshall fall off, at certain excessive current-values, so that theoperating force becomes non-linearly responsive to the current at thesehigh current-values, thus giving my differential relay the well-knownvariableratio response-characteristic.

In Figs. 1, 2 and 3, the current-responsive opcrating-element 16, whichis shown at the botcrating-element it of the relay, the induction diskforces are made to be responsive to substantially the first power of thecurrent, rather than responding to the second power of the current, orto the product of the fluxes produced in the upper and lowermagnet-structures 34 and 35, times the cosine of the angle between them,as

. in ordinary induction-type instruments.-

The falling oil of the first-power current-response of theoperating-torque, at heavy currentvalues, is attained, in Figs. 1 to 3,by building the upper magnet-structure 34 with magnetic crosssectionswhich are sumciently small to produce saturation, commencing with anydesired current-value, this being illustrated in Fig. 2, by

showing the pole-piece tube 38 of the upper magnet-structure 34 as beings aller, in thickness or cross-section, than the correspondingpole-shaped tube 33' of the lower magnetic structure 35, and also byshowing the upper yoke-member 63 as being ring-shaped, so as to have asmaller effective sectional areawith respect to circumferentiallyflowing fluxes, as compared to the solid or diskshaped construction ofthe lower yoke-member 48'. 4

As a result of the structure and combination which I have justdescribed, the differential relay of Figs. 1, 2 and 3 develops anoperating-torque, tending to make the relay respond and close itscontacts "-42, with a substantially rectilinear response to the firstpower of the total current flowing into the bus B, summated over all ofits terminals F! to F8, for current-values up to the point where theupper magnetic structure 34 of the operating-element l8 begins tosaturate, at which time the current-response will fall off, and theoperating-torque will thereafter increase considerably more slowly thanthe current-increases beyond this saturating point.

The normal linear response to current is obtained by the progressivesaturation of the current-transformer 50 which feeds theoperatingelement I8, and at about the time when the upper set of poles38 begins to saturate, the currenttransformer 80 saturates rapidly.Simultaneously with the decrease in the rate of change of the magnitudein the fluxes, during continued increases in the current, as a result ofsaturation, I also obtain a. decrease in the angle between the upper andlower fluxes, in the poles 38 and 38' of the operating-element it, dueto the saturation of the upper poles 38, which still further reduces thetorque produced by the operatingeiement I8. Consequently, during andafter the flnal saturation of the current-transformer 50, practically noincrease in torque occurs, in the operting-eiement IS, with increasingbus-current.

On the other hand, the several restrainingmagnets Ml to M8 developrestraining-forces which are substantially rectilinearly responsive tothe first power of the respective terminal-currents, for allcurrent-values. Thus the proportion or ratio of the totalrestraining-force to the operating-force is constant up to the pointwhen saturation begins to occur in the upper magnetstructure of theoperating-element l8, while beyond this point the ratio ofrestraint-torque to operating torque becomes larger, because of thefalling off of the operating torque with respect to very large currents.This produces the variable-ratio effect which is so desirable in manytypes of differential relays.

When a fault occurs on the bus B, the summation, or vectorial sum, ofall of the currents entering the bus through all of its terminals Fi toF8 will be equal to the fault-current, and the relay is made so that theoperating-force which is developed, under such conditions, will be sum-I ciently strong to actuate the relay, even though the uppermagnet-structure 34 of the operatingelement It is strongly saturatedunder those conditions. In other words, the operating element I 8develops a greater operating-force, even under saturation-conditions,than the sum of the proportional to the current in its feeder, so thatthe sum-total of the eight restraining-forces is very large, while theoperating force developed by the operatingelement i8 will betheoretically zero, because the instantaneous or vectorial sum of theeight said currents will be zero, there being no fault on the bus B, sothat all current which enters the bus must leave the bus.

However, it is well known that the currenttransformers CTI to GT8 willnot, in general, be absolutely perfectly matched with respect to eachother, even at normal load-current values, while, under abnormalcurrent-flow conditions of faultmagnitude, the current-transformers CT!to GT8 will inevitably saturate, in any actual commercial embodiment,and they will begin to saturate at diiferent current-values, and indiflerent degrees or' saturation-characteristics, so that the vectorialsum of the secondary currents on the eight current-transformers CTI toGT8 will not be equal to zero, in the average case, but will indicatethe presence of a fictitious summation-current which is not reallypresent in the bus-terminals TI to T8, but which is actually present inthe operating-element l8 of the differential relay. Because of thisfictitious fault-current in the operating-element it of the relay,resulting from saturation of the line-current transformers CTI to 0T8during so-called through-fault conditions, or fault-conditions outsideof the protected bus B, the operating element I6 is designed to producesaturation in its upper magnet-structure 34, so that it will not developan operatingforce suflicient to overcome the restraint of the eightrestraining magnets Ml to M8 under such conditions. The introduction ofsaturation in the upper magnet-structure 34 of the operatingelement Itmakes it possible to increase the sensitivity of the diflerential relaywith respect to its response to faults on the protected bus B, withoutintroducing erroneous responses to true-fault conditions.

The combination of an electromagnet-type restraint-device or devices,and an induction-type operating-force-producing element is particularlyadvantageous, in differential relay-devices which are utilized toprotect transformers, where heavy asymmetrical magnetizing-currents flowinto the transformer upon the flrst instant of application of powerthereto, as well as being advantageous in the general case, in whichfault-currents, in general, are apt to be asymmetrical in nature, duringthe first few half-cycles of a fault, because of the occurrence of thefault at different times in the voltage-wave of the line-voltage, and atdifferent phase-relations between the faultcurrent and the line-voltage.The result of these asymmetrical currents, whethertransformermagnetizingcurrents or fault-currents, is to produce the sameeffect as if a fairly large direct current were superimposed upon thealternatingcurrent component of the asymmetrical current, thisdirect-current starting out with a large value and dwindling to zeroafter a few cycles, depending upon the conditions of the circuit.

In my novel differential relay, it will be observed that therestraining-torque, which prevents faulty relay-operation, is responsiveto the instantaneous magnitudes of the current, that is, to thedirect-current component plus the instantaneous value of thealternating-current component, at any moment, whereas theoperatingcurrents, which tend to produce a relay-response, beingdependent upon the development of eddycurrents in an induction-disk orthe equivalent, are responsive, selectively, practically to only the theactual structure of the electromagnet-element, and in respect to thecombination which constitutes the differential-relay structure andsystem, I wish it to be understood that many changes in specificembodiments, and permutations of different features, involving omissionsas well as substitutions or additions, may be made as will be obvious tothose skilled in the art. I desire, therefore, that the appended claimsshall be accorded the broadest construction consistent with theirlanguage.

I claim as my invention:

1. An electromagnet-structure comprising a magnetizable core-member, anenergizing-coil means surrounding the core-member, a hat polepiece ateach end or the core-member, each ilat pole-piece having a tapered endextending out away from one side of the core-member, a movable armaturecomprising a, fiat rectangular piece of magnetic material disposedbetween the two tapered ends of the two pole-pieces and separatedtherefrom by airgaps, said rectangular armature-piece beingsubstantially parallel to the core and to the coil-means, and means formovably supporting said armature piece to move toward and away from saidcore and said coilmeans between the tapered ends oi. the polepieces,whereby the tapering 01' said pole-piece ends causes the magnetic fluxto draw the armature-piece toward said core and said coil-means.

2. The invention as defined in claim 1, characterized by thearmature-piece having thickened ends presenting a greatercross-sectional area to the airgaps than the cross-sectional area oi therest of the armature-piece.

3. The invention as defined in claim 1, characterized by thearmature-piece being sufilclently thin to cause the magnetizablematerial thereof to be approaching saturation under an operatingcondition of the device, and also to cause fiuxfringing to increase theefiective airgap-sectlon to at least four times the section oi themagnetizable armature-piece.

4. The invention as defined in claim 1, characterized by saidmagnetizable core-member h'aving a section which varies at differentpoints along the length of the core so as to provide progressivesaturation as the coil-energization increases.

5. The invention as defined in claim 1, characterized by saidmagnetizable core-member having a section which varies at diil'erentpoints alon the length of the core in such manner and degree as toproduce an operating-force, on the armature, which varies substantiallyin accordance with the first power or the energizing-current in thecoil-means, throughout a material operatingrange of current-values.

6. The invention as defined in claim 1, characterized by saidmagnetizable core-member comprising a thin-walled magnetizable tubetapped so as to provide a notched bore in such manner as to provideprogressive saturation in the tube, on increased coil-energization.

7. The invention as defined in claim 1, characterized by saidmagnetizable core-member comprising a thin-walled magnetlzable tubetapped so as to provide a notched bore in such manner as to provideprogressive saturation in the tube, on increased coil-energization, anda magnetizable screw extending partway into the tapped tube from atleast one end thereoi, leaving a region beyond the inner end of thescrew where the tube-material progressively saturates.

8. A multi-torque alternating-current lectroresponsive device comprisinga first torque-producing part and a second torque-producing part, saidfirst torque-producing part comprising at least oneelectromagnet-structure oi the type defined in claim 1, and said secondtorque-producing part-comprising an induction-type electrorespcnsivedevice.

9. A difierential relay for a multi-terminal electrical device to beprotected, said relay comprising a cumulative electro-responsiveoperatingmeans for all of. the terminals to be protected, and aplurality of electro-responsive restrainingmeans, a restraining-meansbeing provided for each one of the plurality of terminals to beprotected; characterized by said operating-means being of a type whichdevelops, in the relay. an operating-force responsive, at times.substantially to the first power of a summation of the terminalcurrentsof the device to be protected, and each restraining-means being of atype which develops, in the relay,'a restraint-force responsivesubstantially to the first power of its own individual terminal-current.

10. An alternating-current differential relay for a multi-terminalaltemating-current device to be protected, said relay comprising acumulative alternating-current operating-means for all of the terminalsto be protected, and a plurality oi. electro-responsiverestraining-means, a restraining-means being provided for each one ofthe plurality of terminals to be protected; characterized bysaidoperating-means being of a type which develops, in the relay, anoperating-force selectively responsive to the alternating-currentcomponent of the vectorial sum of the terminalcurrents, to thesubstantial exclusion of any direct-current component thereof, and eachrestraining-means being of a type which develops, in the relay, arestraint-force responsive to both the direct-current component and thealternating-current component of its own individual terminal-current.

11. An alternating-current differential relay for a multi-terminalalternating-current device to be protected, said relay comprising acumulative altemating-current operating-means for all of the terminalsto be protected, and a plurality of electro-responsiverestraining-means, a restraining-means being provided for each one ofthe plurality of terminals to be protected; characterized by saidoperating-means being of a type which develops, in the relay, anoperating-force responsive substantially to the product 01 twoout-of-phase' alternating fluxes times a function of the phase-anglebetween them, and each restraining-means being of a type which developsa restraint-force responsive substantially to the square of theinstantaneous value of a single flux; in combination with flux-producingmeans, associated with said operating-means, for producing twoout-of-phase alternating fluxes each of which is responsive, at times,substantially to the square root of the vectorial sum of theterminal-currents, and flux-producing means, associated with each 01 therestraining means, for producing a flux 13 which is responsivesubstantially to the square root of the particular terminal-currentindividual to that restraining-means.

12. A diiierential relay for a multi-terminal electrical device to beprotected, said relay comprising a cumulative electro-responsiveoperating-means for all of the terminals to be protected, and aplurality of electro-responsive restrainingmeans, a restraining-meansbeing provided for each one of the plurality of terminals to beprotected; characterized by said operating-means being of a type whichdevelops, in the relay, an operating-force responsive, at times,substantially to the first power of a summation of the terminalcurrentsof the device to be protected, and each restraining-means being of atype which develops, in the relay, a restraint-force responsivesubstantially to the square of the instantaneous value of a single flux;in combination with flux-producing means, associated with each of therestrainingmeans, for producing a flux which is responsive substantiallyto the square root of the particular terminal-current individual to thatrestrainingmeans.

13. An alternating-current diflerential relay for a multi-terminalalternating-current device to be protected, said relay comprising acumulative alternating-current operating-means for all of the terminalsto be protected, and a plurality of electro-responsiverestraining-means, a restraining-means being provided for each one ofthe plurality of terminals to be protected; characterized by saidoperating-means being of a, type which develops, in the relay, anoperating-force responsive substantially to the product of twoout-of-phase alternating fluxes times a function of the phase-anglebetween them, and each restraining-means being of a type which developsa restraint-force responsive substantially to the first power of its ownindividual terminal-current; in combination with flux-producing means.associated with said operating-means, for producing two out-of-phasealternating fluxes each of which a is responsive, at times,substantially to the square root of the vectorial sum of theterminal-currents.

14. An alternating-current differential relay for a multi-terrninalalternating-current device to be protected, said relay comprising acumulative alternating-current operating-means for all of the terminalsto be protected, and a plurality of electro-responsiverestraining-means, a restraining-means being provided for each one ofthe plurality of terminals to be protected; characterized by saidoperating-means being of a type which develops, in the relay, anoperating-force responsive substantially to the product of twoout-of-phase alternating fluxes times a function of the phase-anglebetween them, and each restraining-means being of a type which developsa restraint-force responsive substantially to the square of theinstantaneous value of a single flux; in combination with flux-producingmeans associated with said operating-means, and flux-producing meansassociated with each of the restraining-means, each of saidflux-producing means including a progressively saturablemagnetizable-core portion having I cross-sections which increaseprogressively, for a certain distance along the length of thatcore-portion. from a minimum sectional area that begins to saturate at avery low value of the magnetic flux.

15. A differential relay for a multi-terminal electrical device to beprotected, said relay comprising a cumulative electro-responsiveoperating-means for all of the terminals to be protected,

and a plurality of electro-responsive restrainingmeans, arestraining-means being provided for each one of the plurality ofterminals to be protected; characterized by said operating-means beingof a type which develops, in the relay, an operating-force responsive,at times, substantially to the first power of a summation of theterminalcurrents of the device to be protected, and eachrestraining-means being of a type which develops, in the relay, arestraint-force responsive substantially to the square of theinstantaneous value of a single flux; in combination with fluxproducingmeans, associated with each of the restraining-means, including aprogressively saturable magnetizable-core portion having crosssectionswhich increase progressively, for a certain distance along the length ofthat core-portionffrom a minimum sectional area that begins to saturateat a very low value of the magnetic flux.

16. An alternating-current differential relay for a multi-terminalalternating-current device to be protected, said relay comprising acumulative altemating-current operating-means for all of the terminalsto be protected, and a plurality of electro-responsiverestraining-means, a restraining-means being provided for each one ofthe plurality of terminals to be protected; characterized by saidoperating means being of a type which develops, in the relay, anoperatingforce responsive substantially to the product of twoout-of-phase alternating fluxes times a function of the phase-anglebetween them, and each restraining-means being of a type which developsa restraint-force responsive substantially to the first power of its ownindividual terminal-current; in combination with flux-producing means,,associated with said operating-means, including a progressivelysaturable magnetizable-core portion having cross-sections which increaseprogressively, for a certain distance along the length of thatcore-portion, from a minimum sectional area that begins to saturate at avery low value of the magnetic flux.

17. An alternating-current difierential relay for a multi-terminalalternating-current device to be protected, said relay comprising acumulative alternating-current operating-means for all of the terminalsto be protected, and a plurality of electro-responsiverestraining-means, a restraining-means being provided for each one ofthe plurality of terminals to be protected; characterized by saidoperating means being of a type which develops, in the relay, anoperating-force responsive substantially to the product 01' twoout-of-phase alternating fluxes times a function of the phase-anglebetween them, and each restraining-means being of a type which developsa restraint-force responsive substantially to the first power of its ownindividual terminal-current; in combination with flux-producing means,associated with said operating-means, comprising transformer-meansincluding a progressively saturable magnetizable-core portion havingcrosssections which increase progressively, for a certain distance alongthe length 01 that core-portion, from a minimum sectional area thatbegins to saturate at a very low value of the magnetic flux.

18. An electro-responsive device, comprising a flux-producing meansincluding a progressively saturable magnetizable-core portion havingcrosssections which increase progressively, for a certain distance alongthe length of that core-portion, from a minimum sectional area thatbegins of the flux produced by said flux-producing means; characterizedby said transformer-means including a progressively saturablemagnetizablecore portion having cross-sections which increaseprogressively, for a certain distance along the length of thatcore-portion, from a minimum sectional area that begins to saturate at avery low value of the magnetic flux.

20. An electro-responsive device, comprising a flux-producing meansincluding a magnetizable core-portion comprising a thin-walledmagnetizabletube tapped so as to provide a notched bore in such manneras to provide progressive saturation in the tube, that begins tosaturate at a very low value of the magnetic flux, and a force-producingmeans of a type which is substantially dependent upon the square of theflux produced by said flux-producing means.

21. The invention as defined in claim 20, in

combination with a magnetizable screw extending partway into the tappedtube from at least one end thereof, leaving a region beyond the innerend of the screw where the tube-material progressively saturates.

22. An alternating-current electro-responsive device of a type whichdevelops a force responsive substantially to the product of two out-of-Dhase alternating fluxes times a function of the phase-angle betweenthem, in combination with an alternating-current control-source, andfluxproducing means for producing, in said electroresponsive device, twoout-of-phase alternating fluxes each of which is responsive, at times,substantially to the square root of a current of said control-source.

23. An altemating-current electro-responsive device of a type whichdevelops a force responsive substantially to the product 01. twoout=of-phase alternating fluxes times a function of the phaseanglebetween them, in combination with fluxproducing means for producing twoout-of-phase alternating fluxes in said electro-responsive device, saidfiux-producing means including a progressively saturablemagnetizable-core portion having cross-sections which increaseprogressively, for a certain distance along the length of thatcore-portion, from a minimum sectional area that begins to saturate at avery low value of the magnetic flux.

24. An alternating-current electro-responsive device of a type whichdevelops a force responsive substantially to the product of twoout-of-phase alternating fluxes times a function of th phaseanglebetween them, in combination with fluxproducing means for producing twoout-of-phase alternating fluxes in said electro-responsive device, andtransformer-means for supplying energizing-current to saidflux-producing means, said transformer-means including a progressivelysaturable magnetizable-core portion having crosssectlons which increaseprogressively, for a certain distance along the length of thatcore-portion, from a minimum sectional area that begins i010 saturate ata very low value of the magnetic BERT V. HOARD.

REFERENCES (CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 928,516 Hellmund July 20, 19091,193,678 Fowle Aug. 8, 1916 1,222,431 McCarthy Apr. 10, 1917 1,236,177Jacobs Aug. 7,1917 1,273,940 Smith July 30, 1918 1,503,090 CarichoflJuly 29, 1924 1,610,744 Carichofl Dec. 14, 1926 1,648,674 Carichofi Nov.8, 1927 1,740,536 Breisky Dec. 24, 1929 1,906,027 Wahl Apr. 25, 1933v1,907,804 Hausman et al. May 9, 1933 2,110,673 McConnell Mar. 8, 19382,110,676 Prince Mar. 8, 1938 2,240,677 Sonnemann et al. 1 May 6, 19412,246,548 Sonnemann June 24, 1941 2,303,442 Draper Dec. 1, 19422,318,359 Bellows May 4, 1943

